Document with the error status can be re-routed?

Could you please explain the problem more clearly? Are you referring to a normal K2.net process with SharePoint integration, a Collaboration Tools workflow or some other kind of solution?

Generally, you can handle errors in a process using exception handling as described in various posts on this forum. So if your problem is a normal K2.net process that goes into an 'error' state due to an error during process execution, implement standard .NET exception handling techniques in the code block which will throw the exception, or add a event, activity or process-level exception handler.